Synthesis and spectral properties of novel laser copolymers based on modified rhodamine 6G and 1,8­naphthalimide

Abstract

The excellent photostability of the trichromophoric rhodamine dyes (TCR-1 and TCR-2) containing two 1,8-naphthalimides as antennas had been observed for the solid lasing operation using the dyes in methacrylate. Further understanding of the stabilization mechanism operating in these compounds would require a study of photophysical properties. The fluorescence lifetimes of TCR-1 and TCR-2 have been measured by the single-photon counting technique and the intramolecular singlet energy transfer from the naphthalimide moiety (NA) to the rhodamine moiety (Rh) has been observed. In order to obtain laser dye polymer materials with a high laser-radiation-damage threshold, modified rhodamine 6G molecules (Rh-Al or Rh-Aln) with polymerizable double bonds have been copolymerized with 1,8-naphthalimide derivatives. The absorption spectra of these new copolymers indicate there is little or no interaction between the two NA and the Rh moieties in their ground state, however, the fluorescent spectra indicate that energy transfer from the NA group to the Rh-Al or Rh-Aln group in the copolymers does occur. In comparison, energy transfer was not observed in an equal molar mixture of monomers corresponding to the copolymers, which demonstrated that intramolecular energy transfer in the copolymer synthesized in this study occurred mainly along the polymeric chain.